488
X. Zeng et al.
temperature, the heat is harmful for the sensors. For the reason, rod waveguides are
typically mounted between the materials being inspected and the sensor. However,
after using the waveguide, the characteristic parameters of AE signal may be changed.
So, the results according to these parameters will be influenced.
There are many studies about the influence of rod waveguide on AE signal.
Zelenyak et al. [1] built a finite element method (FEM) model for AE signal propagation in an aluminum plate. A rod waveguide was attached to the plate. The model
was validated by experimental data lastly. In the study, the geometry, material and
temperature of the waveguide are systematically changed to investigate the influence
on the detected signals. The conclusion shows that: the diameter, length and material
of the rod waveguide will predominantly affect the signal, but the temperature has no
significant influence. Sikorska et al. [2] presented the influences of varying waveguide material and/or shape on traditional AE characteristics of pulsed events. Results
show that although ceramic waveguides attenuate the signals more than commonly
used grades of steel and aluminum, waveform fidelity is less affected.
In the above studies, the change of detected signal was studied when the geometry,
material and temperature of the rod waveguide was varied. However, according to
some researches, different frequency signals have different attenuation rules in the
same medium. Besides, the law will have significant impact on the detected signal
transmitting on the waveguide. There are few studies on this aspect. As these factors,
it is necessary to study the influence of a waveguide on AE signals. Besides, as
the waveguide and specimen are made of different materials, the wave will have a
significant change with the variation of frequency when it goes through the interface
between waveguide and specimen. Therefore, it is essential to study the influence of
rod waveguide on AE signal of different frequencies. It was studied in consideration
of the rod waveguide and the interface between rod waveguide and specimen in this
research.
43.2 Relevant Ultrasonic Theory
43.2.1 The Variation of the Attenuation Coefficient
with Frequency for AE Signals
Based on the frequency-power-law dependence phenomenon, Szabo [3] proposed a
generalized frequency-domain model. The model was from the frequency-domain
form of the thermal viscous wave model and the damped wave model. Then, the
frequency-domain acoustic wave model was transformed into a convolution integral
acoustic wave equation in the time domain:
1
c
2
0
∂
2 P
∂t 2 +
2α 0
c 0
L η (P) = ∇
2 P
(43.1)
X. Zeng et al.
temperature, the heat is harmful for the sensors. For the reason, rod waveguides are
typically mounted between the materials being inspected and the sensor. However,
after using the waveguide, the characteristic parameters of AE signal may be changed.
So, the results according to these parameters will be influenced.
There are many studies about the influence of rod waveguide on AE signal.
Zelenyak et al. [1] built a finite element method (FEM) model for AE signal propagation in an aluminum plate. A rod waveguide was attached to the plate. The model
was validated by experimental data lastly. In the study, the geometry, material and
temperature of the waveguide are systematically changed to investigate the influence
on the detected signals. The conclusion shows that: the diameter, length and material
of the rod waveguide will predominantly affect the signal, but the temperature has no
significant influence. Sikorska et al. [2] presented the influences of varying waveguide material and/or shape on traditional AE characteristics of pulsed events. Results
show that although ceramic waveguides attenuate the signals more than commonly
used grades of steel and aluminum, waveform fidelity is less affected.
In the above studies, the change of detected signal was studied when the geometry,
material and temperature of the rod waveguide was varied. However, according to
some researches, different frequency signals have different attenuation rules in the
same medium. Besides, the law will have significant impact on the detected signal
transmitting on the waveguide. There are few studies on this aspect. As these factors,
it is necessary to study the influence of a waveguide on AE signals. Besides, as
the waveguide and specimen are made of different materials, the wave will have a
significant change with the variation of frequency when it goes through the interface
between waveguide and specimen. Therefore, it is essential to study the influence of
rod waveguide on AE signal of different frequencies. It was studied in consideration
of the rod waveguide and the interface between rod waveguide and specimen in this
research.
43.2 Relevant Ultrasonic Theory
43.2.1 The Variation of the Attenuation Coefficient
with Frequency for AE Signals
Based on the frequency-power-law dependence phenomenon, Szabo [3] proposed a
generalized frequency-domain model. The model was from the frequency-domain
form of the thermal viscous wave model and the damped wave model. Then, the
frequency-domain acoustic wave model was transformed into a convolution integral
acoustic wave equation in the time domain:
1
c
2
0
∂
2 P
∂t 2 +
2α 0
c 0
L η (P) = ∇
2 P
(43.1)